The form of tocar doesn’t change in this structure—it will always be simply toca—but the indirect object pronouns in front of toca will change to indicate to whom the responsibility falls.

To your English ear, the me, te, le, nos, os, les may seem unnecessary—especially because the person in question is almost always explicitly stated after the verb form toca, but they are required in Spanish.

Here are the indirect object pronouns used in Spanish:

Person

Singular

Plural

1ª

me

nos

2ª

te

os

3ª

le

les

The bit after the verb tocar adds emphasis and/or clarification.

Because there can be no confusion as to whom the responsibility falls in the expressions me toca, te toca, nos toca, os toca, native speakers will only add the a mí, a ti, a nosotros, or a vosotros when they want to add emphasis. This is the equivalent in English of adding extra stress to the pronunciation, like “It’s your turn.”

Note that in a mí, the mí carries an accent to distinguish it from the word for “my” (eg., mi libro), while in a ti there is no accent on ti because there is no other word with which it could be confused.

In the third person or second person formal, the part after toca clarifies whose responsibility it is. Le toca is ambiguous by itself and could mean “It’s your (Ud., formal) turn”, or, “It’s his turn” or, “It’s her turn.” Thus, the prepositional phrase after toca is necessary to make it clear who is being referenced. For example: